The Zvezda service module was the first fully Russian contribution and the third contribution overall to the International Space Station; it served as the early cornerstone for the first human habitation of the station. It was launched by a Russian Proton rocket in July 2000. Zvezda is similar in layout to the core section of Russia's earlier Mir space station. It is a stepped cylinder 13.1 m long and has two solar arrays with a wingspan of 29.7 m. Zvezda contains three pressurized compartments: a small, spherical Transfer Compartment at the forward end; the long, cylindrical main Work Compartment; and the small, cylindrical Transfer Compartment at the aft end. Space walks can be performed by using the Transfer Compartment as an airlock. Zvezda provided the early station living quarters, and will become the centre of the Russian segment of the ISS as further US and international sections are added. Aside from living quarters, the module provides life support systems, electrical power distribution, data processing systems, flight control systems, and propulsion systems. It also provides a communications system that includes remote command capabilities from ground flight controllers and a docking port for Russian Soyuz and Progress spacecraft and the European Automated Transfer Vehicle.